. An insect crawls up a hemispherical surface very slowly (see the figure)

An insect crawls up a hemispherical surface very slowly (see the figure). The coefficient of friction between the surface and the insect is 1/3. If the line joining the centre of the hemispherical surface to the insect makes an angle a with the vertical, the maximum possible value of ais given

(a) cot a = 3          (b) tan a = 3

(c) sec a = 3         (d) cosec a = 3